The present invention relates generally to optical disks such as CDs (Compact Discs) and DVDs (Digital Versatile Discs), and more particularly to an improved seek control method and device which are useful for a high-speed search for a designated target point on an optical disk that mixedly includes a plurality of areas of different recording densities.
In optical disk drive devices, a so-called xe2x80x9cseekxe2x80x9d operation, as flowcharted in FIG. 9, has been performed conventionally in order to position or seek an optical head at a designated target point. Namely, in response to an instruction to move the optical head from an original or current point (A point) to a target point (B point), the address (expressed in absolute time) of the A point is identified at step S1. Then, a distance the optical head should move is calculated from the addresses of the B and A points at step S2, and the optical head is fed, on the basis of outputs from a linear encoder, to an approximate target point (i.e., a point in the vicinity of the actual target point) at step S3. Once the optical head has been fed up to the approximate target point, the address of the approximate target point is identified at step S4. Then, a specific number of tracks to be crossed by the optical head is calculated at step S5 from the identified address of the approximate target point and the address of the B point. After that, the optical head is further moved to the B point while counting the calculated number of tracks at step S6. Then, at next step S7, the seek operation is terminated upon detecting that the address of the B point has been reached.
However, such a conventional seek operation is disadvantageous in that it would take a long time to search for a designated target point, due to the arrangement that the head feeding operation is initiated only after the distance between the current and target points is calculated on the basis of their respective addresses and the travelling speed of the optical head is limited to a countable range or operating capability of the linear encoder even where the head is to travel or to be fed over a long distance.
Further, whereas the above-mentioned track seek operation achieves a relatively satisfactory result where the track pitch TP is uniform throughout the optical disk as illustrated in FIG. 10A, it is unable to work satisfactorily where the optical disk mixedly includes recording areas of different recording densities such that variation occurs from one pitch TP1 to another pitch P2 as illustrated in FIG. 10B; this is because a difference between addresses of two points can not always be in a simple linear relationship with a distance to be travelled by the optical head. Such a problem would arise not only in the case where the track pitch varies, but also in the case where the recording density varies in both the radial direction of the disk and the direction of jitters as shown in FIG. 11A or where the recording density varies only in the direction of jitters as illustrated in FIG. 11B.
It is therefore a first object of the present invention to provide a seek control method and device for an optical disk which permit a high-speed seek operation of an optical head over the optical disk.
It is a second object of the present invention to provide a seek control method and device for an optical disk which can perform an appropriate seek operation even on an optical disk mixedly including a plurality of areas of different recording densities.
In order to accomplish the above-mentioned objects, the present invention provides a seek control method for an optical disk, which comprises the steps of: dividing an information recording area of the optical disk radially into a plurality of recording areas with a boundary area interposed therebetween, the boundary area being either a high-reflection area that presents a higher reflection light level than the divided recording areas or a low-reflection area that presents a lower reflection light level than the divided recording areas: calculating a distance, from a start point of one of the divided recording areas that contains a designated target point, to the designated target point, when an instruction is given to move an optical head from a current point to the target point over the optical disk; performing a seek operation up to the start point of the divided recording area containing the target point by detecting, on the basis of a variation in the reflection light level, the boundary area located between another one of the divided recording areas that contains the current point and the divided recording area containing the target point; and further performing a seek operation up to the target point on the basis of the distance calculated by the step of calculating.
The present invention also provides a seek control device for an optical disk having an information recording area of the optical disk divided radially into a plurality of recording areas with a boundary area interposed therebetween, the boundary area being either a high-reflection area that presents a higher reflection light level than the divided recording areas or a low-reflection area that presents a lower reflection light level than the divided recording areas, which comprises: an optical head that irradiates a light beam onto the optical disk and detects reflection light from the optical disk; a distance calculating section that calculates a distance, from a start point of one of the divided recording areas that contains a designated target point, to the designated target point, when an optical head is to be moved from a current point to the target point over the optical disk; a boundary signal detector section that detects a boundary signal indicative of the boundary area on the basis of a varying output level of the optical head as the optical head is moved from the current point to the target point; and a servo control section that detects the start point of the divided recording area containing the target point on the basis of detection by the boundary signal detector section and drives the optical head up to the target point on the basis of the distance calculated by the distance calculating section.
The present invention is characterized primarily in that random access is made to the start point of any one of the divided recording areas on the optical disk, by detecting the boundary area on the basis of a level of reflected light therefrom which is chosen to significantly differ from levels of reflected light from the divided recording areas. Thus, if one of the divided recording areas where a designated target point is contained (i.e., a target area) is known, the seek control could be effected properly by just determining a specific number of the boundary areas that are to be crossed, by the optical pickup or head, before the designated target point is reached. With this characteristic arrangement, the present invention allows the seek operation to be initiated immediately without having to calculate a difference between addresses of the target point and an original or current point. Further, the optical head can be moved to the start point of the target area at high speed, because there would occur no substantial limit to the travelling speed of the head, due to the limited operating capability of the linear encoder, before the start point of the target area is reached. Moreover, because the distance between the start point of the target area and the designated target point can be calculated during the seek to the target area start point, the necessary search time can be reduced to a significant degree.
In the seek operation, such as by the servo control section, a position detector is used for a region from the start point of the divided recording area containing the target point to a given point in the vicinity of the target point (i.e., an approximate target point) and then a track counter is used for a region from the approximate target point to the actual target point. In this case, during the calculation of the distance from the current point to the target point, variable control settings for use in the seek control device are adjusted on the basis of recording density information contained in area information. Thus, even where the areas on the optical disk have different recording densities, the recorded information can be read out as soon as the optical head reaches the target area, and it is possible to eliminate the need for pre-gap portions at the beginning of the individual recording areas and also to reduce the necessary search time.
Further, the random access to the start point of the target area does not depend on the recording density at all; what depends on the recording density is the seek operation performed for the region from the start point of the target area to the target point. Because such a seek operation takes place within a same recording area, there would occur no recording density variation. Thus, even where the recording density differs between the individual areas, the distance between the start point of the target area and the designated target point can be calculated with ease on the basis of the recording densities as long as the respective recording densities of the individual areas are known. As a consequence, the present invention can perform an appropriate seek operation even on such an optical disk that mixedly includes various areas of different recording densities.